The evo­lu­tion of glass

DEMM Engineering & Manufacturing - - FRONT PAGE -

THIN GLASS IS REVOLUTIONISING THE PER­FOR­MANCE SPEC­TRUM OF GLASS AND GLASS PAN ES

Thin glass – as thin as a ra­zor blade or a hu­man hair – is a re­li­able method to pro­tect smart­phone touch­screens, sen­si­tive fil­ters and sen­sors. Yet de­spite its ex­treme thin­ness, it is also highly re­silient and scratch- proof. Fur­ther­more, thanks to its flex­i­bil­ity and bend­ing prop­er­ties, it per­mits to­tally new ap­pli­ca­tions in ar­chi­tec­ture, mo­bil­ity and other in­dus­tries. Thin glass is open­ing up new mar­kets and turn­ing vi­sions into re­al­ity.

Just as smart­phones, tablets and e- book read­ers have changed the way we com­mu­ni­cate and con­vey knowl­edge, scratch- proof touch­screens have pro­duced to­tally new qual­i­ties in the man­u­fac­tur­ing of glass, thus en­hanc­ing the per­for­mance of this ma­te­rial which has ac­com­pa­nied the his­tory of mankind’s de­vel­op­ment since the first ad­vanced civ­i­liza­tions. Ul­tra-thin pro­tec­tive glass seems more like film than glass and is so bend­able and flex­i­ble, that it can even be rolled up and trans­ported to cus­tomers on rolls. Spe­cial man­u­fac­tur­ing pro­cesses are now avail­able, al­low­ing for the pro­duc­tion of ul­tra-thin glass films which – at 25 μm (0.025 mm) – are even thin­ner than a hu­man hair or ra­zor blade.

THIN GLASS – MAN­U­FAC­TUR­ING METH­ODS AND DEF­I­NI­TION

The start­ing ma­te­rial for pro­duc­tion is molten glass, which then passes through rollers and is drawn up­ward or down­ward from a tank in what is known as an up-draw or down-draw process. It is then left to cool down on the pro­duc­tion line as a film with the re­quired thick­ness, rang­ing from 25 μm to 10 mm. Along­side these two meth­ods – which, in­ci­den­tally, are older than float glass man­u­fac­tur­ing – thin glass can also be pro­duced with dif­fer­ent spec­i­fi­ca­tions, us­ing over­flow or mi­cro-float­ing pro­cesses. Which­ever method a com­pany chooses, the de­ci­sive el­e­ment for the prop­er­ties of thin glass is the for­mula of the molten glass, which dif­fers from one man­u­fac­turer to another and is a well-guarded trade se­cret.

Thin glass is in de­mand for a wide range of prod­ucts in nu­mer­ous in­dus­tries and can be clas­si­fied quite dif­fer­ently, de­pend­ing on its thick­ness. Whereas in con­struc­tion and ar­chi­tec­ture, glass is con­sid­ered to be thin if it is be­low 3 mm, with vir­tu­ally no rea­son­able or prac­ti­ca­ble use for thick­nesses be­low 1 mm (and no mea­sur­ing in mi­crome­tres). The needs are quite dif­fer­ent else­where. In me­dia tech­nol­ogy, for in­stance, 2 mm glass would be re­garded as rather thick. This in­dus­try com­monly mea­sures thick­ness in mi­crome­tres, and ul­tra-thin glass down to 20 μm tends to be treated as film and shipped on rolls. In the con­struc­tion in­dus­try thin glass can there­fore be pro­duced un­der a con­ven­tional float­ing process where min­i­mal thick­nesses are com­monly around one mil­lime­tre.

The ben­e­fits of thin glass are its ma­te­rial and con­struc­tional qual­i­ties, on the one hand, and its low weight, on the other, e.g. in com­bi­na­tion with other glasses, such as mul­ti­ple in­su­lat­ing glasses. The sta­bil­ity and re­sis­tance of thin glass can be fur­ther en­hanced through chem­i­cal tem­per­ing – some­thing which is par­tic­u­larly in de­mand for dis­plays and pro­tec­tive cov­ers on smart­phones. Other ap­pli­ca­tions are pro­tec­tive cov­ers for mi­cro­scopic in­stru­ments and near-in­frared fil­ters for smart­phone cam­eras.

THIN GLASS IN CON­STRUC­TION AND AR­CHI­TEC­TURE

The con­struc­tion in­dus­try, too, uses thin glasses to cover a wide range of ap­pli­ca­tions where poly­mer so­lu­tions have their lim­its (e.g. the coat­ing on so­lar pan­els). Com­pared with a plas­tic film, glass is far more heat-re­sis­tant, keeps its shape, is gas-tight and has out­stand­ing vis­ual qual­i­ties.

Thin glass is be­ing used more and more for the mid­dle pane in triple glaz­ing, where it al­lows a clear re­duc­tion of thick­ness and weight. A pane struc­ture com­prises an outer float glass pane (4 mm in thick­ness), a semi-tem­pered mid­dle pane (2 mm) and another float glass pane on the in­side (3 mm). Com­pared with con­ven­tional glaz­ing (4/12/4/12/4), this com­bi­na­tion re­duces the weight from 30 to 22.5 kg/m2. The ben­e­fits of light, thin glaz­ing are par­tic­u­larly no­tice­able in re­fur­bish­ment projects.

In ar­chi­tec­ture thin glasses not only re­duce weight, but also ex­cel with their com­bi­na­tion of break­age re­sis­tance and high flex­i­bil­ity, al­low­ing spe­cific cus­tomi­sa­tions. More­over, they per­mit new and vari­able op­tions in shape and de­sign, as it is pos­si­ble to add spe­cially treated coats to thin glass, e.g. through grind­ing or screen print­ing. How­ever, such ap­pli­ca­tions are still more a mat­ter of vi­sion than every­day use. Other for­ward-look­ing ap­pli­ca­tions in­clude in­te­grated func­tional coats such as OPV (or­ganic pho­to­voltaics), where en­ergy is har­vested via win­dows and switch­able PDLC coat­ings (poly­mer dis­persed liq­uid crys­tal). This tech­nol­ogy per­mits the cre­ation of cloudy, opaque view­ing guards which only be­come trans­par­ent un­der an elec­tric cur­rent. One spe­cial­ist in this type of tech­nol­ogy

is the Aus­trian com­pany LiSEC whose vac­uum coat­ing process with dif­fu­sion- proof edge seals also pro­tects func­tional coats from hu­mid­ity and en­vi­ron­men­tal im­pact.

Thanks to thin glass tech­nol­ogy, curved glasses, too, may well be­come in­creas­ingly es­tab­lished in ar­chi­tec­ture. Tem­pered thin glass can be bent into the de­sired shape on site ei­ther through cold bend­ing or in­stal­la­tion bend­ing and can then be used as sin­gle glass or as a coat. It is an in­ex­pen­sive al­ter­na­tive to hot bend­ing at the fac­tory. Fur­ther­more, cold- bent glass has ex­cel­lent vis­ual qual­i­ties, due to fewer dis­tor­tions.

THIN GLASS IN ME­DIA TECH­NOL­OGY AND AU­TO­MO­TIVE EN­GI­NEER­ING

Thin glass in the mi­crome­tre range makes glass par­tic­u­larly flex­i­ble, and in­deed with­out com­pro­mis­ing on sta­bil­ity and hard­ness. One com­pany that spe­cialises in the de­vel­op­ment and pro­duc­tion of ul­tra-thin glass is SCHOTT, which uses its own down- draw tech­nol­ogy. Its pro­ject AS 87 eco has led to what is cur­rently the world’s thinnest glass, at only 25 μm, and is now mass- pro­duced for sen­si­tive ap­pli­ca­tions (e.g. fin­ger­prints) and op­ti­cal com­po­nents (cam­era fil­ters) in smart­phones, where it of­fers re­li­able pro­tec­tion.

The mar­ket for this type of glass is enor­mous. There has been a steady rise in the de­mand for fin­ger­print sen­sors alone and also for spe­cial so­lu­tions to pro­tect such sen­si­tive com­po­nents. Whereas in 2014 the num­ber of units shipped to cus­tomers was 316m, this fig­ure rose to nearly 500m in 2015, and the fore­cast for 2020 is cur­rently as high as 1.6 bil­lion units. Fire­pol­ished pro­tec­tive glass is amaz­ingly hard and is there­fore also used for smart­phone dis­plays. More­over, it is as thin as a ra­zor blade, which makes the pre­ci­sion of the man­u­fac­tur­ing process par­tic­u­larly re­mark­able. With a thick­ness tol­er­ance of only ten mi­crome­tres or less, it prom­ises a high level of re­li­able safety and qual­ity.

Thin glass is also be­com­ing more and more de­sir­able in the au­to­mo­tive in­dus­try – for the in­te­rior, for freely shaped wind­screens and for the cock­pit. Here, too, digi­ti­sa­tion has long been a well- es­tab­lished fea­ture. It is a do­main where highly re­sis­tant, scratch- proof ul­tra-thin glass be­low 250 μm can be used to its full ad­van­tage, par­tic­u­larly in con­vex and con­cave ge­ome­tries. Glass does not age and is there­fore su­perbly suited for the pan­elling of ve­hi­cle in­te­ri­ors. Whereas, in the past, such ap­pli­ca­tions in­volved a risk of in­jury in an ac­ci­dent and were there­fore un­think­able, thin glass has now achieved such a high level of sta­bil­ity, al­most un­lim­ited mould­abil­ity and su­pe­rior op­ti­cal qual­i­ties (e.g. for touch­screens ), that it has opened up to­tally new paths in au­to­mo­tive en­gi­neer­ing and has be­come the al­ter­na­tive to plas­tic. Its op­ti­cal qual­i­ties and ho­mo­gene­ity are far bet­ter, and its chem­i­cal and ther­mal re­sis­tance are so high that it can eas­ily with­stand hu­mid­ity, UV ra­di­a­tion and high tem­per­a­tures.

AN AR­CHI­TEC­TURAL CON­CEPT BUILD­ING BY THE TECH­NI­CAL UNI­VER­SITY OF DARM­STADT, GER­MANY.

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